Telephone system



Jan. 11, 193s. w', MICHAEL@ 2,105,001

TELEPHONE SYSTEM Filed NOV. lI 1935 IN VEN TOR. WALTER MICHAEL/5 A TTORNE Y.

Patented Jan. 11, 1938 TELEPHONE SYSTEM Walter Michaelis, Berlin-Siemensstadt, Germany,

assignor to Siemens & Halske Aktiengesellschaft, Wernerwerk, Siemensstadt, near Berlin, Germany Application November 1, 1,935, SerialNo. 47,786 In Germany November 14, 1934 s claims. (o1. 179-18) VThe present invention relates to automatic telephone systems and in particular to those systems in which the establishment of connecting paths isefected by a special switching operation, for example the operation of an earthing key at the calling station. In order to prevent the particular switching operation from causing undesired switching, as is possible in many systems, and in particular to prevent the earth connected to the subscribers line by the depression of a key, from iniiuencing connecting devices whichhave been taken into use, it has been proposed to allow the call initiating impulses to become operative only on the termination of the switching operation so that the starting relay is not energized until this moment, whereupon it efects the setting up of the connecting path.

The application of this principle, however, involves difiiculties if the starting relay cannot be maintained energized over the subscribers line, either because the subscriber has not yet taken up his receiver, or, in the case of other kinds oi call initiating impulses which promote the setting up of connecting paths in other traflic directions, because neither the energizing nor the holding of the relay can depend upon the completion of the line loop. The known registering of the call initiatingimpulse until a connecting path has been set up between the calling subscriber and an outgoing line, is however only applicable, if, by means of specially constructed switching means, the switching operation (earthing) at the subscribers line occupies so short a time that it is completed before the subscribers line is switched through to the outgoing line, on account of the necessity for preventing subsequent switching devices fromY being influenced by the special switching operation for producing the call initiating impulse, for example the earthing of the subscribers line. The application of specially constructed switching means, in particular earthing keys, is undesirable Vespecially when similar switching operations (earthing) on the part of the subscriber are necessary for other purposes and the differentiation in the exchange between the Various switching operations is dependent upon the duration of the operations. If keys are to be used at the subscribers station and a special key is to be provided for the call initiating impulse it would be necessary in these systems, to provide at least two keys per station.

The use of the known call registering has moreover the disadvantage that if all the lines in the desired traiiic direction are engaged, the call initiating impulse may become operative at a moment when the calling subscriber is not present to complete the call. This has the effect that connecting paths are unnecessarily withdrawn from the general traiiic, including possibly urgent calls, at least for a denite period even if time switching devices are provided for the release.

All these difficulties are avoided by the present invention in that switching means are provided which, under the inuence of the characteristic signal for the termination of the call initiating impulse produced by a special switching operation at the subscribers station, eiTect the registering of the initiating impulse only if there is a free outlet in the desired trafc direction.

One embodiment of the invention is presented in the drawing. The arrangement under con; sideration is a private branch exchange system in which the removal of the receiver initiates the setting up of a local call. When the receiver is removed at telephone N relay T is partially energized over: earth, contact Iy, 2r, resistance W, contact St, over the loop of subscriber N, contact 4t, winding I of relay T, battery, earth. Relay T operates its contacts 5t, Bt, lt, and 8't.

Relay X is connected up in parallel to winding I of relay T, over Contact 5t. Relay X is not energized in this circuit, however, on account of the resistance W. The call initiating impulse is transmitted'to the relay chain of the call finder over contact Gt and the contacts 9:1: and my. The call finder AS is then set on the subscribers connec tion characterized by contact Bt. Relay T is now fully energized over its winding TII and breaks the call initiating circuit at contacts 3i and 4t.

The subscriber N can now bring about the setting of the further connecting devices reached over the call nder AS by dialing impulse trains to establish a connection with another local subscriber.

' If subscriber N desires a connection with the exchange line AL over the exchange selector AW, he merely has to depress his key Ta. The following circuit is thereby set up: earth, key Ta, contact 4t, winding I of relay T, battery, earth. Relay T energizes partially. The closing of contact 5t again connects up relay X in parallel with winding I of relay T and this time relay X opcrates its contacts because the resistance W is not included in its circuit. Relay X opens contact 9:1: and thus prevents relay T from transmitting the call initiating impulse at contact Gt to the relay chain of the call iinder AS. Relay X also closes contact Hx, over which relay Y energizes. At contact |22/ relay Y completes the following locking circuit for relay T: earth, contact |211, resistance WI, contact 5t, winding I of relay T, battery, earth. Relays X and Y are now both energized. Accordingly, contact I3y is closed and contact 14:1: opens. A starting impulse therefore'cannot be transmitted to the relayV chain of the exchange selector AW. Relay X does not deenergize until the subscriber releases the keyTa, this relay being still connected in parallel with Winding I of relay T. With key TaV released relay X deenergizes becauseit cannot hold up in series With Winding I of. relay T or the resistance WI. line free at this time, the callinitiating impulse is transmitted by contact Mx to one of the relays RI R2, etc., vWhich cause a free exchange selector such as AW to be set on the calling subscribers line. If the rstr exchange selector of the series is free the following locking circuit for relayfY and energizing circuit for relay RI is completed; earth, contacts |311, Mfr, winding II of relay Y, contact l5cl, relayRl, battery, earth. Relay RI causes the stepping of the exchange selector AW., The exchange selector AW is advanced until it reaches the contact characterizedby contacts 'It and Iy, When it is brought to rest by the `energizing `of the testing relay CI in the 'known'way (not represented). Contact |5c|V is openedby relay C so that a further startingY impulse cannot be'transmitted to the exchange se-` lector AW.V

, If all the exchange lines are engaged, all the C-contactsUSc, llc, etc) which are connected in parallel, are open.v In'rthisk event the locking circuit for relay Y cannot be set up, when relay X releases. Relay Y therefore deenergizes, and at contact I 2y breaks the locking circuit for relay T. RelayT returns its contacts to normal. Since relay X' which effects the characterizingY ofv an exchange call is common to several or all of the subscribers, the establishment of the starting circuitufor local calls by other subscribers is prevented ,by the opening of contacts Iy and 2x in the case When the characteristic signal has been given for exchange calls by one subscriber sothat there is no chanceof the exchange selector AW being` set' on the connection of another subscriber who by taking up his receiver only gives the starting: impulse for setting up a local: call.

Since in the present arrangement the initiating impulse for setting up an exchangecall is produced merely by the depression yof a key Tw, means can be provided in any Well known manner whereby a signal is transmitted to the calling subscriber after` the exchange selector has been setgon his connecting line to inform him that he-is connected with an exchange line.

g f If a subscriber, either intentionally or unintentionallyioperates his key Ta for a prolonged period a group of the subscribers or all of them are' prevented' from transmitting a call initiating impulse duringthis period. In order toprevent this, time switching` devices, thermo-relays or the If ythere is arf exchange'V like, can be provided with release the condition (relays T, X, and Y energized) produced by the prolonged depression of the key, While at the same time transmitting a signal to the subscriber or toan operator, characterizing the improper use of the system.

What is' claimed is:

1. In a telephone system, a subscribers line, a. local nder and a trunk finder having access to said line, a key, a first and second relay, said first relay operated responsive tothe closing of said subscribers line for starting said local finder to find said line, said rst and second relay operatediresponsive t0 the closing of said subscribersfline While said key is actuated, said second relay Vpreventing the starting of said local finder, a third relay operated responsive to the Operation of said second relay to prepare the starting circuit of said trunk nder, said second relay deenergized responsive to the restoration of said key to complete ther start circuit for starting said trunk nderto, ndsaidli'ne. k

2. In a telephone system, a subscribers substation and line therefor, a local trunk;V a first nder, a toll trunk, a second findena key at said d substation operated before thel receiver is removed at.saidsulostationy and releasedimmedi# ately thereafterwhen a toll .call is made', a relay operated responsive vto the removal of thereceiver'at said substation for completn'glthe' start circuit `for said'rstnder :forv connecting said subscribers line with said local trunk, means in'- cludingsaid relay controlled by' the removal of the' receiver and the momentary operationfof said key for opening the start 'circuit offsaid rst iinderand for preparing thestart circuit of said second finder, and rneans'r'e'spons'ive to the release of said key for completirigthe start circuitffor said second iinder for connecting said subscribers line with said toll trunk.

3. In a ,telephonesystern a subscribers line, a

rst and a second nder having access to' said line, threerelays associated withA saidfline, aj'first of said relays operatedrovera circuit including the. conductors ofsaid line to'start Vsaid "rs'tiinder tond said line vwhen one call is initiated, akey for placingfa ground potential on said line when the subscriber ^desires'tcfextend vvaconnection via said 4second nder, said first *relay operated over a circuitincluding said key andone conductor of said line, aV secondof said relays,` operated in a multiple circuitrwith said first relay, means -responsive to the operation of saidy second relay for completing an-operating circuit for the third of said relays and for preventing the starting, of both nders, said second relay releasing responsive to the restoration of said key immediately afterthereceiver of the subscriber Yon said line is removed for releasing said4 second relayY to start only said second finder to find said line.

WALTER MICHAELIS. 

